1. Field of the Invention
The present invention relates to a lead frame conveying apparatus for conveying a lead frame between guide rails which are extended parallel. The present invention also includes a transverse conveying mechanism used in the lead frame conveying apparatus and a method of converting an elliptic motion performed in the transverse conveying mechanism into a rectangular motion.
2. Description of the Related Art
FIG. 5 is a perspective view showing a conventional apparatus for conveying a lead frame. In the drawing, a lead frame 1 is transferred between two guide rails 2 and 3 by a frame receiving arm 4. For example, when the lead frame 1 is transferred from the guide rail 2 to the guide rail 3, the frame receiving arm 4 is moved in the order of A--B--C--D shown by arrows in the drawing. The guide rails 2 and 3 comprise two rails 2a, 2b and 3a, 3b, respectively, which are extended parallel. A linear guide bearing 11a is slidably mounted on a liner guide rail 11 on a base block 21, a bearing block 20 being fixed to the linear guide bearing 11a through a holder 5. A shaft 6 is passed through a bearing hole (not shown) in the bearing block 20 so as to connect the frame receiving arm 4 and a plate 7 and is fitted in the bearing hole so as to be axially slidable. The shaft 6 is provided at either side of the linear guide rail 11. The plate 7 has a lower end member 8 which is downwardly extended and on which a rolling bearing 9 is provided. An extension coil spring 10 interposed between the bearing block 20 and the plate 7 produces the force to upwardly move a portion comprising the frame receiving arm 4, the shafts 6, the plate 7, the member 8 and the rolling bearing 9. A guide plate 13 is attached to two linear guide bearings 12a, 12b which are vertically slidable and which are provided on the base block 21 so that the guide plate 13 contacts with the rolling bearing 9 which is upwardly moved by the coil spring 10. Extension coil springs 10a, 10b are respectively provided between the guide plate 13 and the base block 21 at both ends of the guide plate 13 so as to constantly generate the force to upwardly move the guide plate 12 (the coil spring 10a is not shown in FIG. 5). A rolling bearing 13a in rolling contact with a vertically moving cam 14 is provided at the center on the side of the guide plate 13, which is opposite to the side thereof engaged with the linear guide bearings 12a, 12b. The vertically moving cam 14 is eccentrically provided on the rotational shaft of a motor 16. A timing belt 18 placed over timing pulleys 19a, 19b is driven by a pulse motor 17. The connecting member 20a provided on the bearing block 20 holds the timing belt 8 therein so as to connect the bearing block 20 and the timing belt 18. The base block 21 is fixed to a base plate 22. FIG. 6 is a side view showing the basic operation of the frame receiving arm 4 of the conventional frame conveying apparatus in the case where the lead frame 1 is transferred from the guide rail 2 to the guide rail 3. When the lead frame 1 is conveyed to the guide rail 2 by an external apparatus (not shown), the frame receiving arm 4 positioned below the guide rail 2 is upwardly moved for scooping up the lead frame 1. The frame receiving arm 4 is transversely moved from a position above the guide rail 2 to a position above the guide rail 3 while holding the lead frame 1. The frame receiving arm 4 is downwardly moved for placing the lead frame 1 on the guide rail 3. The frame receiving arm 4 is then transversely moved from a position below the guide rail 3 to a position below the guide rail 2. The frame receiving arm 4 performs such a one-cycle motion. Each of the guide rails 2 and 3 is partially cut off to form a space which allows the frame receiving arm 4 to scoop up the lead frame 1 on the guide rail and place the lead frame on the guide rail, as shown in FIG. 5.
The operation of the conventional apparatus for conveying a lead frame is described below with reference to FIGS. 5 and 6. The frame receiving arm 4 waits for the lead frame 1 at point A. When the lead frame 1 is fed to the guide rail 2, the motor 16 is driven, and the vertically moving cam 14 eccentrically provided on the rotational shaft of the motor 16 is thus rotated. The rolling bearing 13a provided on the guide plate 13 is vertically moved while making rolling contact with the periphery of the vertically moving cam 14 by virtue of the coil springs 10, 10a, 10b in accordance with the distance between the portion of contact with the periphery of the vertically moving cam 14 and the rotational shaft. This causes the whole guide plate 13 to be vertically moved. When the motor is driven, and when the guide plate 13 is upwardly moved according to the rotation of the vertically moving cam 14, a portion comprising the rolling bearing 9, the lower end member 8 and the plate 7 is upwardly moved. The frame receiving arm 4 connected to the plate 7 by the shaft 6 is thus upwardly moved to point B so as to scoop up the lead frame 1 from the guide rail 2. The motor 16 is stopped at half rotation. A predetermined number of pulses are then applied to the pulse motor 17 from an external pulse generator (pulse motor driver) according to the distance between the guide rails 2 and 3 so that the pulse motor 17 is driven. When the timing pulleys 19a, 19b are rotated by driving the pulse motor 17, the timing belt 18 is rotated following the rotation of the pulleys 19a, 19b. The rotation of the timing belt 18 is converted into a transverse horizontal linear motion of the bearing block 20 through the connecting member 20a. The portion comprising the frame receiving arm 4, the bearing block 20, the connecting member 20a, the shaft 6, the plate 7, the lower end member 8 and the rolling bearing 9 is thus horizontally moved from point B to point C in the transverse direction. When the motor 16 for driving the vertically moving cam 14 is then half rotated, the guide plate 13 is downwardly pushed by the vertically moving cam 14, and at the same time, the rolling bearing 9 is also downwardly pushed. The frame receiving arm 14 is consequently downwardly moved to point D so as to place the lead frame 1 on the guide rail 3. When the pulse motor 17 is driven to rotate in the reverse direction, the frame receiving arm 4 is returned to point A to complete one cycle.
In the conventional apparatus for conveying a lead frame configured as described above, since the frame receiving arm must be horizontally positioned with high accuracy according to the positions of the guide rails, the pulse motor is used. However, the pulse motor driver is required as an external apparatus for driving the pulse motor. The conventional apparatus thus has the problem that the need for two motors for vertical and horizontal motion increases the cost of the apparatus.